Since Edison began to engage in scientific inventions, it can be said that he has been very successful, and he is indeed gratified in his thirties. But there is a problem that has been lingering in the mind and has not been solved for a long time, and that is how to use electricity to reduce people's labor burden.
In the late summer of 1878, Edison was again considering the potential uses of electricity in Menlo Park. As early as the autumn of 1877, he had done several experiments with incandescent lamps, but because many people were exploring this field at that time, Edison gave up research in this area. Of course, the invention of the phonograph was also one of the reasons why he left the research on incandescent lamps.
During the period when Edison was exploring electric lights, society's lighting problems were basically solved by gas lights. However, gas lamps have their own inherent shortcomings, such as insufficient brightness, easy leakage, and poor supply system. Later, someone developed the arc lamp in an attempt to replace the gas lamp, but after experiments it was found that it could not be widely used. The reasons were firstly that its light was dazzling; secondly, the distance between the carbon poles had to be constantly adjusted; thirdly, after the carbon poles were ignited, There will be a choking smell and black smoke. This determines that it cannot be used for indoor lighting. But despite these shortcomings of arc lamps, some countries have made limited use of them since the 1850s, such as for navigation beacons or street lighting.
There are many people trying to break the gas monopoly on lighting. However, they all face the problem of how to bridge the huge gap between theory and practice. In theory, all that is needed to make an electric light is a thin filament, which can be made of carbon or other materials. As long as the filament is sealed in a glass container and the air is removed, the electric current can be passed through to make the filament emit incandescent light. However, it is not that easy in practice. It is necessary to find a material for making filaments that is not easy to burn out, and to ensure that the glass container is a good vacuum. Even if these necessary conditions are clarified, it is difficult to create an ideal electric lamp in the superior equipment of the laboratory. What's more, there are many other problems that need to be solved urgently to implement commercial large-scale production.
In the autumn of 1878, when Edison conducted his first set of experiments, he focused on testing more than 50 different raw materials to emit light in a vacuum after being made into filaments and carbonized. Finally, he concluded that the problem of electric light was solved. , there is only one way, that is, the resistance of the filament should be high and the heat dissipation should be slow.
After that, Edison made great efforts, but the carbon wire experiment showed no signs of success, so he turned to platinum and platinum-like metals because these materials met the requirements of high resistance and slow heat dissipation.
After countless experiments, platinum filament seems to be the most ideal filament among other metals. So in early October, Edison filed a patent application for a platinum wire "electric light".
After the first incandescent lamp patent was filed, Edison smelled victory. But he was well aware that there were many difficulties ahead, so he began to work harder. He realized that his mathematical foundation was not enough. If he wanted to successfully design an incandescent lamp and make it a key part of the lighting system, he would have to perform a series of complex calculations. Therefore, before the end of the year, he hired two mathematicians, and after their rigorous calculations, they proved that Edison's intuition was correct: electric lamps must have a resistance of more than 100 ohms before they can become rivals of gas lamps.
A year or two later, Edison had made initial achievements in the manufacturing of incandescent lamps. In the fall of 1879, Edison received a new Springer air pump that allowed him to create a vacuum of one hundred thousandth of an atmosphere. Due to the improvement of vacuum conditions, Edison instinctively used carbon filament as a filament material for experiments. Edison believed that carbon filament was the ideal filament material from the beginning. He gave up this material only because the previous vacuum was not enough and the carbon filament melted too fast.
Starting from October 16, after five days of exploration, the final breakthrough occurred. This time Edison used cotton thread. He put the cotton thread into the U-shaped groove carved on the nickel plate and carbonized it for several hours. He and his assistant Batchelor had been working in the laboratory for several days, because the carbonized carbon wire was so thin and brittle that it was accidentally broken twice before putting it into the light bulb.
On the third time, they finally put the carbon filament into the light bulb, then removed the gas from the light bulb, sealed it, and passed the current through. The long-awaited scene appeared!
Edison increased the power The first bulb burned for several hours, the second bulb burned for 40 hours, and the test continued for two days. Edison knew that he had overcome the difficulty. He said: "I think we have found a way to make it. If it can last 40 hours now, in a few days I can make it last 100 hours."
Within two weeks, Edison filed a patent application for a carbon filament electric light. Over the next few weeks, work began in Menlo Park to manufacture the light bulbs. Because Edison continued his experiments—continuously changing the size and shape of light bulbs, and changing the methods of introducing filaments and sealing bulbs—not all light bulbs manufactured at the time were the same. In addition, Edison's colleagues made many replicas of these light bulbs. Some were hung in the laboratory, and some were sent to Edison's home, Mr. Batchelor's home and local cheap hotels. Telegraph poles were then erected to connect the lights to the lab's generator. There are also some light bulbs suspended above the street. After nightfall, only the electric lights glowed brightly, and people from the surrounding countryside, who could come here on foot or on horseback, came to enjoy this novel scene.
Edison was very good at publicizing his activities. This was not only the instinct of a good businessman, but also a heartfelt enthusiasm. When major newspapers across the United States published a large number of reports on the invention of the electric light, Edison immediately seized the opportunity and announced that the laboratory would be open to the public after Christmas. As a result, the Pennsylvania Railroad set up a dedicated line in Menlo Park. Within a few days, Edison saw an extraordinary sight.
Due to the constant flow of visitors, a laboratory that accommodates twenty or thirty technicians has been suspended for a week. These visitors came from all directions, filling this small town with a radius of several miles with vehicles of all kinds, and thousands of men, women, and children flocking here. At the same time, bankers, brokers, capitalists, tourists, and agents eager to do business got off the train.
There are also many visitors clamoring to have a word with this great man. Some visitors ignored the dissuasion on the "warning signs" and started playing with the machines without authorization. Among them, an expensive air pump and other equipment were damaged in this chaos. By January 3, 13 bulbs had been lost, and Edison had to announce that from now on, visitors would not be allowed to enter the laboratory without permission.
If these side issues are excluded, the Menlo Park exhibition can be said to have achieved effects that ordinary exhibitions cannot achieve. It proved to people that incandescent light was indeed feasible, that an indoor revolution triggered by it would be inevitable, and that the era of gas and arc lighting was coming to an end. The night will become colorful from now on.